Fluorescent display device



Sept. 2l, 1954 J. l.. swlTzER FLuoREscENzr DISPLAY DEVICE 2 Sheets-Sheetl Filed Dec.l 28, 1949 ,.1 .Q ..1 ,iiilllllllllllllllllllllllllllllllllllll l v n l.

ATTO NEYS J. L. SWITZER FLURESCENT DISPLAY DEVICE sept. 21, 1954 2Sheets-Sheet 2 Filed Dec. 28, 1949 INVENTOR Josn/I L-Swfzer BY ATTgZl-fsHb M y Patented Sept. 21, 1954 UNITED STATES PATENT OFFICE FLUORESCENTDISPLAY DEVICE Joseph L. Switzer, Cleveland Heights, Ohio ApplicationDecember 28, 1949, Serial No. 135,388

(Cl. Vo-71) 14 Claims.

This invention relates to fluorescent display devices or signs in whichthe symbols or other indicia comprise fluorescent materials and moreparticularly to such signs which are illuminated by a source ofiluorescigenous radiations disposed at the edge of the display or sign.

Fluorescent displays and signs are highly desirable since they givegreater brilliance of colors, greater color contrasts and more pleasingeffects than conventional, non-fluorescent signs which selectivelyabsorb and reiiect different wavelengths of incident visible light.

Previous eiforts to provide inexpensive, eiiicient and simplefluorescent signs have failed either because the devices are toocomplicated and expensive -due to the need for a large source ofiiuorescigenous radiations or because the ultimate elfect of thedisplays are not unlike the usual non-fluorescent signs.

It is generally desirable to direct the light beam onto a sign at assmall an angle of incidence as conveniently possible to obtain thegreatest amount of illumination, whether the sign is made ofnon-fluorescent or fluorescent materials. In the latter case, of course,a source of iluorescige- Vnous radiations is used. All commercialsources k of this type normally emit both visible light and ,blacklightf or ultraviolet light. When a fluorescent sign is illuminated withboth types of light, much of the visible light will be reflected in theusual manner not only from the fluorescent materials on the sign butalso from the nonfluorescent materials which are generally used forbackground portionsV of the sign. This results in a low contrast ratiobetween the different portions of the sign thus destroying a major partof the effectiveness of the fluorescent sign.

On the yother hand when only ultraviolet light is to be used forillumination, the source of radiations must be provided with lters forblocking out the visible light. These filters however, also block out asmuch as 50% of the desired ultraviolet radiations. Thus, to obtain therequisite amount of illumination, a much larger source of radiations isneeded, which obviously increases installation and operating expense ofthe display device. Furthermore, since as small an angle of incidence aspossible is required for normal Viewing of the sign, it will be seenthat large overhanging structures are necessary for proper positioningof the larger sourceof radiations and larger lters with respect to thedisplay.

Another disadvantage of iiuorescent signs in which the radiations aredirected toward the sign at as small an angle of incidence as possibleis that some of the ultraviolet radiations are refiected to the eye ofan observer. These reflected ultraviolet radiations cause the eye, whichis susceptible to them to fluoresce to such an extent that theappearance of the sign is foggy and hazy.

Display devices and signs according to the present invention overcomethese various disadvantages and provide displays in which the contrastratios are of a high order and which can be brilliantly illuminated bysmall commercial sources of fluorescigenous radiation without the needfor ltering out the visible radiations.

it is an object of the present invention to provide an edge-lightediiuorescent sign which utilizes both ultraviolet light and visible lightwhile at the same time obtaining a high contrast ratio and greatbrilliance.

According to the present invention symbols or other indicia made of afluorescent composition or material are disposed in optical contact withthe rear surface of a transparent panel. A small but efficientcommercial source of radiations having wave lengths from about 35100 toabout 4500 is disposed at one edge of the panel so that the radiationswill pass longitudinally through the panel while being internallyreflected at the surfaces thereof. An example of a source of radiationswhich has been found to be very efficient and effective in the presentinvention is a fiuorescent tube known as the type 360 BL tubemanufactured by the General Electric Company. This tube producesradiations in the violet-blue portion of the visible spectrum and alsonear ultraviolet radiations, i. e., near the visible portion of thespectrum. The radiations emitted by this tube have wave-lengths varyingfrom about 350D to about Li500 a great proportion of the radiationsbeing in the ultraviolet range and having a wave length of 3650 Thistube is not equipped with lters for eliminating the visible radiations.

All of the radiations pass through the panel and strike the fluorescentindicia which is in optical contact with a surface of the panel and areconverted to those wave-lengths in the visible .spectrum which arecharacteristic of the particular fluorescent material upon which thelight impmges.

The fluorescent materials which may be employed in the present inventionare compounds which are known as daylight iiuorescent compounds. Thesecompounds project visible light of a predominant wave band or color whenexcited by visible and invisible radiations of a shorter wave lengththan the predominant wave band.

These colors are very bright due to the fact that they selectivelyreilect a substantial proportion of the dominant wave band which ispresent in the incident visible light and, in iiuorescent response tothe shorter wave lengths of incident light, emit light of substantiallythe same wave band as is selectively reflected. The sum of the reflectedand emitted light in the predominant Wave band constitutes .theprojected light, which may be greater than the `total amount of light`of the dominant wave band which is present inthe incident light. Thus,such compounds may project as much as 120 to 130% of the red light whichis present in incident white light. Heretofore, dyes or 'pigments whichreflected as much as 60% of the red light in the incident white lightwere 'regarded as extremely brilliant red materials. Such ycompounds aredescribed in application No. 575,364, iiled January 30, 1945, by JosephL. Switzer and Robert C. Switzer.

Perhaps one `of the greatest advantages to be derived from the presentdisplay device is vthe fact that there lcan be no Yreilected or `emittedlight whatever fromithe area surrounding the indicia. These areas, ofcourse, lare free from all kinds of material, ine., they areconstituted'solely by the clear uncoated 'transparent panel so that allthe radiations are-internally reected within the panel in these rarcasthus rendering the socalled background areas completely light-free andthus invisible to an observer.

The present invention, therefore, provides `a sign or display inwhichthe indicia has the lgreatest possible contrast `with thebackground areas and in which the indicia has a brilliant appearance,composed essentially of pure colors. The effect is comparable totheefect obtained when bright sunlight shines idirectly vthrough stainedvglass windows.

If desired the `indicia may be composed of a l single iiuorescen'tmaterial so that Va monochromatic sign is obtained. This might besuitable when lettering and Vwords are to be displayed. However, byusing a variety of different iluorescent materials anydesired object orscene can be provided in `brilliant colors. Practically any shade ofcolor can be provided by mixing different materials. vSigns or displaysof this type are exceedingly lifelike and vpossess a warmth and depth ofcolor not obtained in other kinds of signs. f

The iiuorescent 'materials may be coated directly onto the rearsurfaceof the transparent panel'in'the desired pattern orthey'canbeapplied to a ilexible sheetof vfabric or paper or the likelocated behind the panel. In the latter'case the fluorescent materialsmay be aiixed to the lsheet in patterns and these patterns placed inoptical contact vwith the panel or the materials maybe affixed to asubstantial area of the sheet and the pattern lformed-by placing-onlyYportions of the coated area in optical contact with the panel. In anyevent only those portions of thev sheet disposed in optical contact withthe surface of the panel willbe illuminated. The remaining portions ofthe sheet, which are not in optical contact with the panel, whethercoated-with uores- 4cent material or not will not be Ailluminated by theradiations transmitted through thepanel as described above. They would,of course, be illuminated by extraneous'visible'light which might`st'rike'the front ofthe panel at a 'small angle of incidence.

The invention will-now be'describedin greater detail with reference tothe accompanying drawings, in which,

Figure 1 is a front view of a display device according to the presentinvention, with a portion broken away to show the source ofillumination,

Figure 2 is an enlarged vertical cross-section of the device taken alonglines 2-2 of Figure 1,

Figure 3 is an enlarged front elevation of a portion of the device withcover removed to show source of illumination,

Figure 41is an kenlarged cross-section of a portion of the panel showingfluorescent material applied thereto,

Figure 5 is a rear elevation of a modied form 'of the device, partlybroken away to show various details,

Figure 6 is an venlarged cross-section of a part of the device, taken'along the line 6-6 of Figure 5,

Figure 7 is an enlarged cross-section of a portion of the panel takenalong line 'l-'i of Fig- 'ure.5,

Figure 8 iis `an enlarged cross-section of `a spor- `tion of a modifiedpanel for use in Athe display device.

Acording vto the ln'xodiiication lshown in Figures l to vLl, inclusive,the display device comprises -apanel -l of glass, transparerrtplasticmaterial or lotherzclea'r transparent rmaterial :capable of'transmitting radiations within the range of vrfrom about 3.500 f. l'toYabout '4500 A design or other indicia f2 is provided "on the back -ofthe panel l I asdescribed'rriore 'fully hereinafter. `A light source i3emitting fluorescigenous radiations, as, for example, Lthe type 3'60vBlftube previously mentioned, is located near thelower edge of thepanel H vwithin a 'housing llt having a removable cover `I 5 as shown inFigure 2.

The panel `Il is provided ywith an yopaque backing member I6which-'shields the `panel l! from extraneous 'light 'coming from behind-the device. A U-shaped frame 11 "holds the pan-el H and backing memberI5 'securely Vtogether 'to form a panelunit'thus protectingv'theindicia-on the rear surfaceof the panel il. The frame -l'fl'extends'across the top of `the panel and down the sides to a point near thebottom `edge of `the panel il. This frame `in -additionto securing thepanel unit ytogether also prevents the escape of -visible'ilig'ht fromthesides'a'nd top of the panel.

The housing Ilincludes fa bottom lportion It and a top "I9 v-vvhich isprovided with ya vlongitudinally extending hanged vslot 2U adapted toreceive the lower vedge `of the panel and backing member vvH5 as shown.Aresi-lient packing 'Z is provided between the panel `unit and thevflanges of the slot 26 to precludethe escape of light 'exceptthrough'the pan-l H. l:Space-:i stopl members E22 are secured to the`underside of the v"top le of lhousing lll beneath the slot 2i] vtolimit the distance the panelunit'can 7be inserted into the slot. lThetube I3 islocatedcentrallybeneath the bottom edge of panel 'I'I and'fissecured in place by Vconventional soeketsS 'a-tthe endsof the'housingIll.

rlhet'op ofthe panelunit-is -held in place `by a bracket 2# r`providedwith a channel adapted Vto receivethe top-of'fthelirame VI. The bracket24, and the'housing IM #may :be secured, as lshown, yby any conventional'means to a support, such asa wall'25 or the like.

The conventional l.electrical .equipment for fluorescentytubes'su'c'htasthe electrical -ballast 25 and cable "21 -are ydisposedwithin kthe housing as shown.

The radiations from the ftubel3 which enter the bottom edge of panelIIpass throughthe panel, being internally reflected from the surfaces ofthe panel, until they strike the indicia I2 provided on the rear surfaceof the panel as optical contact with the panel, i. e., so there is no lmof air therebetween. It is highly desirable to also apply a layer 29 ofWhitek material suchL as white paint on the layer 28. This extra layer`improves the luminescence of the display by refleeting lvisible lightwhich is emitted by the fluorescent material. It will be clear that bothlayers 28 and 29 must be in the form of the indicia. The backing memberI6 generally consists of a dark material or is coated with a layer 39 ofdark colored material, such as flat black paint or the like, whichreflects as little light as possible, so that extraneous visible lightaccidentally falling upon the display device willnot reduce the contrastwith the indicia. Since the dark layer 30 is not in optical contact withthe panel I I, there being at least a film of vair therebetween, thepassage of the radiations Within the panel II will not, of course, beinterrupted as when they strike the fluorescent layer 28 which is inoptical contact with the panel.

The modification shown in Figures 5 to 7 `inclusive differs from thefirst modification only in the manner in which the indicia are' disposedin optical contact with the panel I I. The other elements of the deviceincluding the source 0f radiations I3 and associated elements are thesame as in Figures l, 2 and 3.

In this modification, however, the indicia are not applied directly andpermanently to thepanel I I but rather are applied to a flexible sheetwhich is removably aixed to the panel II. Referring specifically toFigure '7 a flexible sheet 3Ic`om posed of paper` or fabric or the likeis provided with a base layer 32 of reflective material such as whitepaint inthe form of the desired pattern. A layer 33 of fluorescentmaterial, also in the form of the pattern, is superimposed on thereflective layer 32 and then a layer -34 of a pressureadhesivesubstance, such as the so-called rubber cement, is applied on thefluorescent layer 33. The uncoated portions ofthe sheet 3I arepreferably of a dark-non-reflective color.

This sheet can be afxed to the back of the panel II simply by applyingpressure so that the indicia will adhere to the panel. Since no lm ofair is between the surface of the panel and the fluorescent layer 33,said layer is in optical contact with the panel and will function asinthe previously described modification. To more securely x the sheet tothe panel a band pf adhesive material may be applied all around theedges of the panel.

One great advantage of this type of arrangement is that the sheet may bequickly and easily removed and another sheet having different indiciasubstituted therefor. y

)This modification also enables one to provide a sign or display whichcan be seen from both sides. For example, if a transparent sheet or filmis used in place of fabric or paper 3| and if the reflective layer 32 isomitted, the visible light emitted by the fluorescent material will beprojected not only through the panel I I, as shown inthe drawings, butalso rearwardly through the transparent sheet, thus making the indiciavisible from the back also.

A third modification of the present invention;l

is shown in Figure 8. Here the sheet 3I is provided with layers ofreflective material 35, nuorescent material 36 and adhesive material 31over substantial areas of the sheet, and not merely at the location ofthe desired indicia. In order to obtain optical contact at the desiredpoints so as to produce the desired display, the sheet is pressed ontothe panel at those points where luminescence is desired to form thepattern or sign. This arrangement has the advantage that the display maybe changed merely by stripping the sheet from the panel and applyingpressure a second time at those areas which constitute the new indicia.This system is, of coures, most suitable where substantiallymonochromatic displays are preferred. When colored pictures or scenesare` desired the type of indicia described in connection with Figures 4and 7 are required.

In each of the above modifications, the panel I I through which theradiations are transmitted by internal reflection to the fluorescentmaterial, is preferably formed of a solid, hard, clear material capableof transmitting radiations having wave-lengths lying within the rangeextending from about 3500 through the major proportion, and preferablythrough the entire visible light spectrum. The panel may be made ofglass or a hard synthetic polymeric or plastic material. Most commonglasses have satisfactory radiation transmission characteristics as wellas certain organic polymers such as polymethyl methacrylate, celluloseacetate, polystyrene, other vinyl polymers, etc.

The 'fluorescent materials `which may be ernployed in the presentinvention may be of various kinds. In general,l they comprise a carrierma.- terial having dispersed therein or thereon one or more substancescapable of uorescing and emitting visible light when exposed toradiations having wave-lengths lying between 3500 and 4500 Thosefluorescent materials which are disclosed in application Serial No.455,610, filed August-21, 1942, by Joseph L. Switzer, Robert C. Switzer,and Richard A. Ward, U. S. Patent No. 2,417,384, of Robert C. Switzer,and application Serial No. 575,364, filed January 30, 1945, by Joseph L.Switzer and Robert C. Switzer, are particularly satisfactory. Theseapplications disclose fluorescent materials which comprise carriershaving dispersed therein organic compounds which iluoresce brightly indaylight. Such materials also emit brilliant visible light when exposedto radiations of wave-lengths lying in the range extending from about3500 up to about 4500 and hence are excellently adapted to use in thepresent invention.

The following organic dye compounds may be employed. The fluorescentcolor for each ccmpound is also indicated.

Meta diethylaminophenol phthalein hydrochloride Red Metadiethylaminophenol succein hydrochloride Red Meta m o n e t h y laminophenol phthalein hydrochloride Orange The ethyl ester of metamonobutylaminophenol phthalein Orange Meta aminophenol phthaleinhydrochloride Yellow green Di (para` dimethylaminophenyl) ketone iminehydrochloride Yellow green 2,3, diphenyl 'N-phenyl quinox- Y aloniumsulphate Green p,p Di Ep (p aminobenZoylamino) benzoylaminol stilbene.

o, o di [sodium sulphonatel--. Blue Meta m o n oY-ethylamino'phenolpl'itl1a1ein l Orange Meta m o n o ethylaminophenol phthaleinVethylester hydrochloride Orange Diamino stilbene di sulphonicY acid(sodium-salt) Blue-White 2, amino, 9(4 aminophenyl) acridonium nitrateYellow-green 4, amino 1,8 naphthal p-xenylimide Yellow-green 2, [4 amino8 carboxynaphthyl (l) benzimidazole sodium sulfonate Green Di(dimethylaminophenyl) phenyl amino naphthyl methene chloride Green 4methyl,l 7 hydroxy coumarin i sodium salt Blue' Such compounds maybedispersed or dissolved in suitable carrier materials. which` are highlytransparent to radiations of Wave-lengths lying between about which haveindices of refraction similar to those of glass or synthetic resins usedas the panel material. Such carrier materials may becertain soluble orthermoset organic polymeric materials, noncrystallized saccharides andnoncrystallized polyhydric alcohols. Examples of suitable solublepolymeric` 'materials useful as carriers are polymeri'zed methyl, ethyl,and butyl methacrylates, polystyrene, polyvinyl ace'- tate, celluloseacetate, ethyl cellulose, and similar compounds. polymeric compounds arepolymerized melamine formaldehydev resins, polymerized urea form.-aldehyde resins particularly alcohol-modified urea formaldehyde resinscontaining no plasticizers, and similar compounds;

glucose and sorbitol.

As set forth in applicationv Serial No. 455,610, the fluorescentmaterial constitutes a solidified carrier material having dispersedtherein atleast one such fluorescent organic'compound in a con'-entration of not more than iiv'e perl cent for blueemitting 'compoundsto not more than oneV per cent for red-emitting compounds. Particularlygood results are obtained when one uses a maximum concentration of from.025 gram for compounds emitting yellow-green light and .015 gram forcompounds emitting red light, per cubic centimeter of carrier material;the thickness of the layer of nuorescent material being such that theweight of the iiuorescent compound per square centimeter of surface doesnot exceed .0005 gram for `each spectral Wave band of light emitted.

Fluorescent compositions may be applied in the form of coatings. If thecarrier is a soluble compound, the material may be mixed in suitableproportions with a suitable volatile solvent to form a liquid coatingmaterial which may be applied by painting, printing, or screeningprocesses. Evaporation of thesolvent leaves a solid layer oflfluorescent material.

If the carrier is a thermoset plastic material, partially polymerizedcarrier material, or the reactants necessary to produce the polymer, and

35Go and about 4500 andv Examples of suitable'thermose't Examples ofsuitable saccharides and polyhydric alcohols are thev fluorescentcompound in proper concentration, are incorporated in a suitable liquidwhich is applied'to the surface. The resulting coating is baked toremove any volatile liquids present and to form a layer of iiuorescentcomposition containing the fluorescent compound dispersed in a thermosetpolymer.

The fluorescent compound may be incorporated in sheets of organicmaterial, such as fabric or paper sheets or the like instead of beingdispersed in carriers. Such fluorescent sheets may be of the typedescribed in U. S. Patent No. 2,417,384, of Robert C. Switzer. Such dyedsheet materials are particularly well suited for use as the flexiblesheet illustrated in Fig; 8'.

Inorganic fluorescent pigments may be employed instead 4of organicfluorescent compounds. Examples of suitable inorganic Apigments are theactivated alkaline metal sulphides. These pigments may be dispersed in aliquid carrier and applied tothe desired base in the manner indicatedabove.

Ihe carrier material for the fluorescent dye or pigment may be such thatit is tacky and will have adhesive properties. AV flexible sheet havingone vor more-areas-coated with such fluorescent material may ybeemployed inthe devices described in connection with Fig. 5 to Fig. 8.

However, it is moreadvantageous to employ a separate layer of'permanently tacky, pressure adhesive material over the fluorescentmaterial, as described 'above' withrelation 'to Figs. 5-8.

The elongated body through which the radiations are transmitted byinternal reflection may have other forms than'that of a rectangularpanel shown in the illustrated embodiments. For example, the 'panel' maybe V-shaped in verticalcros's `s'ecti'onwiththeradiations passing intothe 'thickrendof 'the Vpanel and being internally reflected from theconvergingsurfaces until the angles of 'incidence become less 'than the'critical angle 'of reflection'. The radiationswill then pass through'a'surfa'ce' 'of andout of vthepanel in a relatively Wide area. Thefluorescent material maybe disposed inoptic'al Contact with thesurface'of the panel, either in the area where the radiationsp'asfs'through the surface, or in the area Where' there is normallyinternal reflection of the radiations.' By -this means, a greaterintensityofradiation and fluorescence may 'be obtained at points'remotefrom 'the source of radiation than can bebbtained `with panels havingparallel sides Vor 'an'added pleasing effect can be obtained inthe formof 'a' glowor haze at the top ofthe 'display at an area substantiallyremoved from the source of radiations.

While 'the fluorescent material has been disclosed 'as beingcoated'on'asurface of the panel or disposedon a flexible'sheet adjacent the panel,the fluorescent material may also be disposed in recesses or channelsformed ina vsurface of the panel 'to provideunusual eifects whenirradiated.

The present' invention' thus provides display devices whichvAov'eic'o'm'e' the shortcomings of prior devices illuminated byfluorescigenous radiation, and make possible for the rst time a compact,inexpensive,l efficient display device in which the patterns are formedof fluorescent materials irradiated by iluorescigenous radiation to emitbrilliant, glowing visible light of many colors.

Various modifications may be made in the devices described above withoutdeparting from the spirit of the present invention. The scope 9 of thepresent invention is defined by the appended claims.

What is claimed is:

1. A fluorescent display device comprising a transparent panel capableof transmitting fluorescigenous radiations and having opposed continuoussurfaces, a source of unltered fluorescigenous radiations disposedadjacent the edge of said panel so that said unfiltered radiations maybe transmitted without interruption through the panel by internalreflection from the surfaces thereof, and fluorescent material inoptical contact With selected areas of one of said opposed continuoussurfaces of the panel whereby visible radiations are emitted from saidmaterial when excited by the fluorescigenous radiations and asubstantial portion of said emitted visible radiations pass withoutinternal reflection through the areas of the opposed surface oppositesaid selected areas to which the uorescent material is in opticalcontact.

2. A device as claimed in claim 1 wherein the fiuorescigenous radiationsfrom said source include radiations having wave lengths within the rangeof from about 3500 to 4500 3. A device as claimed in vclaim 1 whereinthe fluorescent material is applied directly to the surface of thepanel.

4. A device as claimed in claim 1 and further comprising a lightreflective material superimposed on the uorescent material in opticalcontact with said panel.

5. A device as claimed in claim 4 and further comprising a backing sheetof dark color disposed behind said panel and said fluorescent materialand light reiiective material.

6. A device as claimed in claim 1 wherein said panel is composed ofglass.

7. A device as claimed in claim 1 wherein said panel is composed of aclear, transparent plastic material.

8. A device as claimed in claim 1 wherein the fluorescent material isresponsive to daylight.

9. A uorescent display device comprising a transparent panel capable oftransmitting fluorescigenous radiations and having opposed continuoussurfaces, a source of uorescigenous radiations disposed adjacent theedge of said panel, so that said radiations may be transmitted withoutinterruption through the panel by internal reflection from the surfacesthereof, a flexible sheet of dark color disposed behind said panel,iiuorescent material aliixed to said sheet and facing said panel, apressure adhesive material superimposed on said fluorescent material foradhesion to said panel at selected areas so that said fluorescentmaterial will be in optical contact with said panel at said selectedareas, whereby visible radiations are emitted from said material whenexcited by the fluorescigenous radiations.

10. A device as claimed in claim 9 wherein said uorescent material isaffixed to said sheet only at said selected areas.

11. A device as claimed in claim 9 further comprising a light reflectivematerial disposed between said fluorescent material and said flexiblesheet.

12. A device as claimed in claim 11 wherein the light reiiectivematerial, the fluorescent material and the adhesive material are aiiixedto the exible sheet and are superimposed on each other in the ordernamed only at said selected areas.

13. A device as claimed in claim 9 wherein the iiuorescent material andthe adhesive material substantially cover said flexible sheet andwherein said adhesive material is adhered to said panel only at selectedareas.

14. A device as claimed in claim 9 wherein the fluorescent material isresponsive to daylight.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 1,813,491 Gillard July 7, 1931 1,850,319 Fensom et al. Mar.22, 1932 2,097,625 Langlotz Nov. 2, 1937 2,223,409 Dixon Dec. 3, 19402,247,409 Roper July 1, 1941 2,358,203 Best Sept. 12, 1944 2,358,867Madan Sept. 26, 1944 2,417,384 `Switzer Mar. 11, 1947 2,548,126 SholkinApr. 10, 1951 FOREIGN PATENTS Number Country Date 401,151 Great BritainNov. 9, 1933 402,825 Great Britain Dec. 11, 1933 OTHER REFERENCES BlackLight Applied to Plastic Signs, Modern Plastics, pp. 144, 145, April1946.

